24/7 Emergency Plumbing & Heating Services
$25 OFF Your First Service | Use Code: 907SAVE
5655 Gate Keeper Ave, Anchorage, AK 99504
Calculate required diaphragm expansion tank size in gallons for hydronic heating closed boiler loops and domestic potable water heaters.
Under ASME sizing standards, a typical residential hydronic heating system with 40 gallons of system water (12 PSI cold fill, 30 PSI relief valve) requires a 4.4-gallon expansion tank (such as an Amtrol Extrol #30). A closed 50-gallon domestic water heater requires a 2.1-gallon thermal expansion tank (Amtrol ST-5).
Adjust inputs for real-time results
Boiler water volume or water heater tank capacity.
Standard boiler cold pressure is 12 PSI; domestic water is 50 PSI.
Minimum Expansion Tank Volume
Note: Air pre-charge in the expansion tank must be adjusted to match static system pressure before connecting to plumbing.
Water is non-compressible; as water heats and expands in a closed loop, hydrostatic pressure spikes until the safety relief valve discharges.
Common questions regarding this calculation and code compliance
A 50-gallon domestic water heater with incoming water pressure up to 60 PSI requires a standard 2.0 to 2.1 gallon thermal expansion tank.
